AgCl coating. Please explain black vs gray coating

[Trent A. Basarsky]

Hello,

After doing electrophysiology for quite a few years, I was asked a 
fundamental question that I realized I could not answer.

When you AgCl a Ag wire for electrophysiolgy, I have been taught that a 
black coating is desirable.  When I coat my wires I constantly reverse the 
polarity of the wire being coated, and it alternates between a gray andblack 
coating.  I take the wire out after leaving it in the black coating phase for 
a while.

My question is:  What is the difference between the gray and black coating?  
I get the gray coating when my wire is postive, thus I presume the 
Cl- is being plated on.  Why is the black coat desirable?

For your info I AgCl my wires in weak HCL using a 1.5 V D battery with a 
polarity switch on it.

Thanks for any info, e-mail preferred.

Trent



__________________________________________________________________
Trent A. Basarsky			tab at iastate.edu
Department of Zoology & Genetics
Iowa State University
Ames, Iowa 50011
(515) 294-4054